Has anyone improved their VO2 max?

Long runs (2/3kms) with hr >130 for a few weeks should help you in improving vo2

Stop smoking too

Pick up a cardio rich sport like football/ultimate frisbee/badminton. (Find games on Playo). Not only will that gradually improve your cardio vascular fitness but also (hopefully) pull you away from smoking. Sustainable, fun shit.
I have been playing football regularly for over 7 years now. Helps a lot.